1. Field of the Invention
The present invention relates to a polygonal mirror which is used in an optical beam scanning system, to a manufacturing process thereof, and to a mold used for manufacturing the polygonal mirror.
2. Description of Related Art
A polygonal mirror which has a plurality of reflective facets for deflecting an optical beam to a beam receiving surface is used in an optical beam scanning system.
Conventionally, a polygonal mirror has been made of aluminum alloy or optical glass. However, when aluminum alloy or optical glass is used, a large number of processes, including milling and grinding, or polishing, are required to realize a high quality polygonal mirror. The necessity of such a large number of processes results in high manufacturing cost. In addition, since the polygonal mirror made of metal or glass is heavy, a complicated and expensive drive system is required for driving the polygonal mirror at high speed.
Recently, therefore, resin has been tried to make a polygonal mirror in an injection molding method as disclosed in Japanese Patent Laid Open Publication Nos. 63-229421 and 63-304223. However, this method has not been developed enough to guarantee high quality optical characteristics, and particularly flatness of the reflective facets of the polygonal mirror.